HIV infection induces a spectrum of neurological disorder in at least two thirds of patients with AIDS. In addition to behavioral and motor abnormalities, these manifestations are histologically apparent as multifocal giant cell encephalitis and diffuse white matter degeneration. Although microglia are the major reservoir of HIV in CNS, brain tissue exhibits extensive pathogenic alterations including apoptosis of neurons, reactive astrocytes, cytolytic destruction and demyelination. The pathogenesis of HIV in CNS involves changes in virus infected cells, which are manifested in cytokine dysregulation and release of viral factors. One of the factors which has received considerable attention is the HIV Tat protein. Tat is released from infected cells and can serve as a transactivator of cellular as well as viral promoters. The ability Of Tat to be released and taken up into cells permits this protein to function in a dysregulatory capacity through autocrine and paracrine pathways. Tat activates gene expression not only through its own LTR, but can also activate transcription of other viral promoters, notably the JCV late promoter. JCV, a human papovavirus which is the causative agent of PML, infects oligodendrocytes and its replication is increased in patients with HIV associated PML. Our hypothesis is that HIV Tat protein released from infected microglia activates JCV through a paracrine mechanism. Oligodendrocytes are rarely, if at all, infected with HIV, although we have observed this cell type to contain a significant amount of Tat protein in brain tissue of AIDS patients with PML. In our proposed studies we will develop an in vitro model consisting of co-cultures of HIV infected primary microglia and JCV infected primary oligodendrocytes to investigate the intercommunication between H~V-l-infected microglia and JCV-infected oligodendrocytes via Tat protein. Based on our preliminary studies, activation of both JCV and HIV by Tat requires a cellular protein, Puralpha. Puralpha is an activator of both JCV and MIV transcription and mediates the action of Tat through the formation of a ternary complex consisting of Puralpha, Tat, and RNA. Our proposed studies will investigate the role of Puralpha interaction in MIV and JCV gene expression and replication in primary microglia and oligodendrocytes respectively. These studies will further investigate the mechanism of Puralpha interaction through RNA in order to develop protein based therapeutics which will block the action of Tat in promoting HIV and JCV infection.